Sample analyzing monitor and combustion control system using the same.
1. Field of the Invention
The present invention relates to an calibrating process for analyzing a sample and a device therefor, and particularly to a sample analyzing monitor in which dioxin and related compounds contained in combustion flue gas resulting from incineration of non-industrial waste and industrial waste, exhaust gas from metal refining processes, exhaust gas from cars, or the atmosphere are detected to determine the concentration of the dioxins or the dioxin precursors in the flue gas or the atmosphere; and a combustion control system in which the results from the monitoring by means of the monitor are used for combustion control.
2. Description of the Related Art
It is known that dioxins are contained in exhaust gas from metal refining processes, exhaust gas from cars, or waste liquid from a bleaching process of pulp or the like. The word xe2x80x9cdioxinsxe2x80x9d is a general term of polychlorinated dibenzo-p-dioxins (PCDDs) having 75 kinds of isomers and polychlorinated dibenzofurans (PCDFs) having 135 kinds of isomers. A broad sense of the word includes coplanar polychlorinated biphenyl (coplanar PCBs). Dioxin and compounds related thereto are abbreviated to xe2x80x9cdioxins congenersxe2x80x9d hereinafter.
Findings on the mechanism of generation of dioxin congeners have been accumulated (BUNSEKI, 1998, pp. 512-519). Conditions for generating dioxin congeners varies greatly, dependently on sites, the mechanism of the generation thereof and so on, and are highly complicated. It is considered that in a combustion process at high temperature in an incineration plant or the like, de novo synthesis is an influential mechanism of generation of dioxin congeners. In the de novo synthesis, a chloride of a metal such as cobalt, iron or copper in fly ash functions as a catalyst so that carbon reacts with chlorine. In the basic reaction of the de novo synthesis, carbon atoms, chlorine atoms and oxygen atoms which coexist at high temperature are subjected to radical reaction so that not only dioxin congeners but also many organic chlorine compounds such as polychlorinated benzene congeners and polychlorinated phenol congeners are produced. The produced polychlorinated benzene congeners and polychlorinated phenol congeners turns to precursor congeners of dioxin congeners. It is said that the precursors turn to dioxin congeners. It is also said that in an incineration plant, dioxin congeners are generated mainly by two processes. One thereof is a process in which dioxin congeners are generated upon imperfect combustion inside a combustion furnace, the combustion temperature of which is lower than 800xc2x0 C. The other is de novo synthesis inside a boiler or a dust collector at a temperature of 250-550xc2x0 C.
Various measures are taken to reduce the generation of dioxin congeners in incineration plants as much as possible. To suppress the discharge of dioxin congeners to surroundings, it is desired that combustion conditions are improved or techniques for removing dioxin congeners efficiently are developed. However, much time and labor have been required for the development of the techniques for suppressing the discharge of dioxin congeners. For example, the following process has been conducted: the process of combusting wastes under a certain condition, determining the concentration of dioxin congeners in flue gas or fly ash under this condition, obtaining a correlation between the combustion condition and the amount of the generated dioxin congeners, and searching an optimal combustion condition or an optimal removal condition from the correlation.
In order to monitor the operation situation of actual incineration plants, there has been recently suggested a process in which the concentration of dioxin congeners, which have a very low concentration, is not directly measured but an alternative substance which has a relatively high concentration is assayed and then the concentration of the dioxin congeners is estimated from the result of the assay. Examples of such a technique include processes and devices disclosed in the Bulletin of Institute of Environmental Science and Technology of Yokohama National University (Vol. 18, 1992), JP-A-Nos. 4-161849, 5-312796, 7-155731, 9-015229 and 9-243601.
In the techniques disclosed in the Bulletin of Institute of Environmental Science and Technology of Yokohama National University (Vol. 18, 1992) and JP-A-Nos. 4-161849 and 5-312796, polychlorinated benzene congeners are measured by gas chromatography (GC) and are used as an index of alternatives of dioxin congeners. The dioxin congeners are estimated from the correlation between the two.
In the technique disclosed in JP-A-7-155731, dioxin congeners and so on contained in combustion ash are thermally decomposed by heating the ash, so as to reduce the dioxin congeners and so on. Polychlorinated benzene congeners and polychlorinated phenol congeners in the ash before and after the heating are analyzed to estimate the elimination ratio of the dioxin congeners. In this manner, the condition for the thermal decomposition is optimized.
In the technique disclosed in JP-A-9-015229, the concentration of polychlorinated benzene congeners in flue gas and that of polychlorinated phenol congeners therein are measured and then the concentration of dioxin congeners is calculated from a dust concentration and flue gas retention time which are measured in another way and the above-mentioned concentrations.
In the technique disclosed in JP-A-9-243601, polychlorinated benzene congeners and polychlorinated phenol congeners in flue gas are subjected to real-time measurement, and the concentration of dioxin congeners is continuously obtained. The flue gas is introduced to a laser ionizing mass spectrometer to ionize the flue gas. The flue gas is subjected to mass spectrometry. Thus, the concentrations of the polychlorinated benzene congeners and the polychlorinated phenol congeners are obtained. At last, the concentration of the dioxin congeners is indirectly calculated.
JP-A-9-55185 discloses a manner of calibrating the concentration of dioxin congeners in the case that the effect of impurities having a high concentration or measuring conditions such as ionization voltage are changed at the time of analyzing a sample continuously for a long time.
It is expected that the generation of dioxin congeners from incineration plants is reduced by a dioxin-reducing manner based on improvement in combustion conditions, adoption of a removal technique, or the like. However, it is indispensable to measure, at a real time, how much dioxin congeners are reduced by such a dioxin-reducing manner. From such a viewpoint, the above-mentioned methods have the following problems.
Each of the Bulletin of the Institute of Environmental Science and Technology of Yokohama National University (Vol. 18, 1992) and JP-A-Nos. 4-161849 and 5-312796 discloses a manner of analysis, but does not disclose any specific technique for measuring polychlorinated benzene congeners or the like quantitatively. This technique is essential for such monitoring.
JP-A-7-155731 does not disclose any specific technique for measuring polychlorinated benzene congeners, polychlorinated phenol congeners or the like quantitatively. The technique disclosed in JP-A-9-015229 does not have a clear basis of a relationship equation between dioxin congeners and polychlorinated benzene congeners, polychlorinated phenol congeners or the like, which is a premise of the invention. Moreover, this publication does not disclose any specific technique for analyzing these substances quantitatively.
JP-A-9-243601 suggests a possibility of real-time measurement of the concentration of polychlorinated benzene congeners, but does not disclose any specific manner for measuring this concentration.
In JP-A-9-55185, a sample used for concentration-calibration is a material which is the same as a target trace gas. For the calibration, therefore, it is indispensable to stop the introduction of a sample of the target trace gas. Thus, JP-A-9-55185 does not disclose any technique in which an analysis step and an calibration step are simultaneously performed. JP-A-9-55185 also have a problem that in the case of measuring a minor constituent gas in flue gas by mass spectrometer, the mass spectrometer is affected by impurities such as hydrogen chloride, sulfur oxide and nitrogen oxide present in the flue gas so that ionization efficiency changes; and a problem that the target trace gas to be measured adheres to laying pipes from an inlet to a mass spectrometer or a filter so that the concentration of the target trace gas near the inlet becomes different from the concentration thereof introduced to the mass spectrometer.
An object of the present invention is to provide a process and a device making it possible to measure the concentration of a target trace gas in gas containing various impurities while the concentration is calibrated moment by moment and to realize a real-time analysis at a high precision on line.
The present invention has been made to attain the above-mentioned object. The present invention relates to a process in which as a calibration means in an online monitor using mass spectrometry, a material having substantially the same ionization efficiency as a target trace gas, for example, a stable and rare isotope of the target trace gas is added, as an internal standard, at a constant concentration, and then the amount of the ions is measured; and a device therefor.
Specifically, the concentration of the target trace gas is calibrated and quantitatively measured as follows.
(1) An internal standard having properties, such as ionization efficiency and vapor pressure, similar to the target trace gas is introduced at a constant concentration to the side of an incineration furnace of a pretreatment section of a monitor, and then the ion strength ratio of the target trace gas to the internal standard is measured to determine the target trace gas quantitatively.
In this way, it is possible to correct an error resulting from a change in the ion strength on the basis of effects of impurities and an error resulting from a change in the concentration on the basis of adhesion of the target trace gas to pipes in the middle and the pretreatment section. As a result, the target trace gas can be quantitatively measured.
(2) While the amount of waste gas introduced from an incineration furnace to a monitor is monitored to calibrate a change in the amount of an introduced target trace gas based on a change in the amount of the introduced waste gas, an internal standard having properties, such as ionization efficiency and vapor pressure, similar to the target trace gas is introduced at a constant concentration to an ion source of the monitor. In this way, the ion strength ratio of the target trace gas to the internal standard is measured to determine the target trace gas quantitatively.